The invention relates to a device for simultaneously separating a multiplicity of wafers from a hard brittle workpiece and to an associated method.
To separate wafers from a hard brittle workpiece, wire saws are known which operate with a sawing slurry (cutting lapping) and others in which abrasive grains are securely bonded to the saw wires (abrasive cutting). As an alternative to saw wires, saw bands and parting blades are also used as tools.
Abrasive cutting using diamond-studded saw wires is used predominantly for making individual cuts. It is possible to distinguish between installations which operate with a coiled, open-ended individual wire and those which operate with an endless wire turning at high speed. With these methods, simultaneous multiple cuts are not possible.
Diamond wire sawing using a multiply coiled, finite individual wire is described in application DE 19851070, which has not yet been laid open for inspection. This application describes a method and a device for simultaneously separating a multiplicity of wafers from a hard brittle workpiece, the workpiece being passed through the wire web formed by a saw wire by a translational relative movement, perpendicular to the longitudinal axis, between the workpiece and a wire web of a wire saw, with the aid of an advancing device. In this invention, the workpiece is rotated about the longitudinal axis while the wafers are being separated.
Despite a large number of advantages, this method also has specific disadvantages:
A precondition for the device to function correctly is that a separate wire-guidance system be present, which is formed from at least two reels for coiling and uncoiling the wires and a plurality of tensioning and guide rolls. Owing to the abrasive grains which are securely bonded to the saw wire, the diamond saw wire is very brittle and of low elastic deformability, making coiling and uncoiling difficult.
Owing to their low elasticity, their high brittleness and high mechanical stress concentration, the diamond saw wires are highly sensitive. This mechanical sensitivity promotes damage and cracks in the wires at tensioning and guide rolls.
Wire lengths of several kilometers are required. In the prior art, availability of such lengths in sufficient quantities and quality does not exist or is very restricted.
A reciprocating multiple wire saw with diamond-tipped tool is described in U.S. Pat. No. 4,727,852. In this fixed abrasive slicing technique (FAST technique), the longitudinally oriented saw wires are tensioned in a frame which executes a translational, oscillating movement through the workpiece, which is itself rocking about an axis oriented perpendicular to the wires, so that the short contact length between saw wire and workpiece is intended to ensure an acceptable separating rate.
The object of the present invention is to provide a device which provides an improved sawing method for simultaneously separating a multiplicity of wafers from a hard brittle workpiece having a longitudinal axis.
This object is achieved by a device with a wire web made from saw wire and with an advancing device which brings about a translational relative movement, which is perpendicular to the longitudinal axis of the workpiece, between the workpiece and the wire web of the wire saw, in the course of which movement the workpiece is passed through the wire web, wherein the wire web is formed from a multiplicity of individual wires, and wherein there is a device for holding and rotating the workpiece about the longitudinal axis.